There have been many attempts in the past to improve the safety accorded to occupants of automobiles when involved in an accident. A portion of these attempts have dealt with the provision of various safety devices in the passenger compartment, most commonly by implementing passenger restraint systems such as safety belts and/or harnesses. However, during the 1970s some automobile manufacturers began supplementing these typical passenger restraint systems with air bags located throughout the passenger compartment to enhance the safety features of the automobile.
Many developments were made regarding the use of air bags during the 1970s, partially as a result of an increased awareness of the need for increased passenger safety as well as in anticipation of possible government regulations requiring that air bags be employed in all automobiles. Although a large amount of development was directed towards automobile air bags during this time period, due to various factors, these activities subsided and have only again begun to increase.
The general concept of an automobile air bag is to provide an inflatable structure that is responsive to an impact which will inhibit the forward motion of a passenger to reduce the likelihood of suffering severe injury when involved in an accident. Although the air bag is quite simple in concept, there have been numerous developments regarding the manner in which the air bag is inflated, including regulation of the flow rate of the materials injected therein.
Many air bag inflators utilize a single, decaying flow rate during inflation once an appropriate signal is received from a collision or other similar detector. U.S. Pat. No. 3,895,821 to Schotthoefer et al., issued July 22, 1975, discloses an inflation apparatus for an air bag safety device which uses only a single charge initiated by an electrical signal. In this apparatus, there is an outer cylinder containing a volume of gas under pressure. At the end of the cylinder nearest the inflatable apparatus, namely the air bag, there is a second inner cylinder with a propellant charge. There is a disk isolating the propellant in the inner cylinder from the outer cylinder. The disk also covers discharge ports connecting the outer cylinder to the manifold which is connected to the air bag. Upon sensing a collision, the propellant charge is ignited which causes the rupturing of the disk. Thereafter, the propellant gases mix with the gas in the outer cylinder and gas begins to flow into the air bag through the ports connecting the outer cylinder to the manifold. Although the Schotthoefer at al. patent discloses using a single electrical signal for deploying an air bag with ignition of a propellant to expand the gas, there is no disclosed delay between an initial flow rate into the air bag and a subsequent increased flow rate into the air bag.
U.S. Pat. No. 4,018,457 to Marlow, issued Apr. 19, 1977, discloses an air bag safety apparatus which offers one inflation rate for low impact collisions and a second for high impact collisions. The Marlow apparatus includes an outer containment which stores a gas under pressure for inflating an air bag. Enclosed within this outer containment is a propellant containment which stores a propellant charge. In a low impact collision, one ignitor activates the propellant charge, causing an increase in pressure within the propellant containment. This increase in pressure eventually ruptures a disk which isolates the propellant containment from both the outer containment and a ramming member. Upon rupture of this disk, exhaust gases from combustion of the propellant charge mix with the gas stored in the outer containment. In addition, the rupture also directs the ramming member towards a disk which ultimately isolates the outer containment from the air bag. The ramming rod breaks this disk and allows the mixed gases to flow into the air bag. The operation of the apparatus for a high impact collision merely adds the additional step of firing a second ignitor which, summarily, causes the propellant charge to burn at a faster rate, thereby providing a higher flow rate into the air bag. Regardless of whether one or two ignitors are activated in the Marlow apparatus to ignite the propellant, the activation is ultimately produced by an electrical signal. Furthermore, even though the Marlow patent discloses two flow rates into an air bag, one for low and a second high impact collisions, there is no disclosed means of increasing the flow rate into an air bag after an initial volume of material has been injected therein.
Although not specifically designed for an air bag system, U.S. Pat. No. 3,731,843 to Anderson, Jr., issued May 8, 1973, discloses an inflating apparatus which allegedly provides a substantially uniform rate of inflation. The apparatus generally includes a housing which is essentially separated into two compartments. The first contains a compressed gas while the second contains an ignition assembly and propellant. A bladder fluidly connected to the second compartment extends into the first compartment, when inflation of an article is desired, a discharge assembly fluidly connected to the first compartment is manually activated and gas from the first compartment begins flowing to the inflatable member. However, a portion of this gas is also directed to the ignition assembly within the second compartment to cause its activation. Activation of the ignition assembly involves the acting of the pressurized gas on a convexly-shaped, domed spring. After a predetermined pressure develops on the convex surface of the domed spring, it pops or snaps into a reversed position to essentially engage a firing pin and percussion primer assembly to ignite the propellant. As the propellant burns, the bladder is inflated, thereby reducing the volume of the first compartment to allegedly provide a more uniform flow of gases from the first compartment into the inflatable member.
A second general category of air bag inflators offer an initial flow rate to partially inflate the air bag which is followed by a second increased flow rate to complete inflation. The manner in which this delayed, increased flow rate is initiated has been the subject of many development efforts in the industry. For instance, U.S. Pat. No. 4,050,483 to Bishop, issued Sept. 27, 1977, discloses an inflation apparatus which incorporates a surge delay. In this apparatus, there is a cylinder containing a volume of gas under pressure. At the discharge end of this cylinder, a rupture disk separates the cylinder from the manifold connecting the cylinder to the air bag. The rupture disk is coupled with a device capable of generating a force sufficient to break the rupture disk. When a collision is sensed, a signal is sent to the device to rupture the disk and thereby allow gas to begin to flow from the cylinder, through the discharge manifold, into the air bag. The rate of deployment of the air bag at this juncture is reduced since the flow of gases prior to the ignition of the propellant charge does not generate sufficient pressure to rupture a disk located in the manifold's main flow channel. Consequently, the initial flow of gases is diverted through secondary flow channels in the manifold. Upon breakage of the rupture disk allowing the initial flow of gas into the air bag, there is a predetermined time delay after which a second electrical signal is sent to the end of the cylinder opposite the discharge manifold to activate a propellant charge contained in an isolated chamber. Upon ignition of this propellant charge, a disk isolating the propellant charge from the cylinder is ruptured and the propellant gases flow into the cylinder, mixing with the gases contained therein. Coinciding with this mixture, gas continues to flow out of the cylinder through the manifold. As the propellant charge burns, pressure within the cylinder will increase sufficiently to break the disk in the manifold's main flow channel. Consequently, the flow rate of the gas into the air bag reaches a maximum level. Although the Bishop patent discloses a variable deployment rate for inflation of an air bag, the variable deployment rate is the result of two electrical signals, one of which is used to rupture the main isolation disk and the second of which is used to ignite the propellant after a predetermined time delay.
U.S. Pat. No. 3,966,228 to Neuman, issued June 29, 1976, discloses an air bag restraint system in which the rate of deployment of the air bag varies over time by using differential pressures to provide a delayed, increased flow rate. In one embodiment of this invention, there is a first cylinder containing a certain volume of gas under pressure. A manifold connects the first cylinder to the air bag, but a disk having charges contained wherein prohibits flow of gases therebetween. At an end opposite of this disk is a second cylinder in communication with the first cylinder by means of an orifice. The second cylinder thus also initially has gas under pressure equal to that within the first cylinder. When sensors detect a collision, an electrical signal is sent to the charges within the disk. The explosion causes the disk to break and gas begins to flow into the air bag, including gas from the second cylinder which flows throuqh the orifice, into the first cylinder, and then into the air bag. Since the cross-sectional area of the orifice is smaller than that of the manifold connecting the first cylinder and the air bag, the pressure in the second cylinder will not decrease as rapidly as the pressure in the first cylinder. When a certain pressure differential between the first and second cylinders is achieved, the piece containing the orifice will break. Upon the breaking of this portion, the flow rate of the gas from the second cylinder into the first cylinder, and eventually into the air bag, will be increased to a maximum level. Although the Neuman patent discloses a variable deployment rate from a single electrical signal, together with the use of a pressure differential, there is no disclosure or suggestion of using the pressure differential for the ignition of any type of propellant. Therefore, in order to fully inflate the air bag, a larger volume of gas is needed since no heat is being applied to expand the gas and thereby increase the pressure and flow rate. Relatedly, it is likely that larger cylinders would be required to store the gas to ensure full inflation of the air bag.
U.S. Pat. No. 3,948,540 to Meacham, issued Apr. 6, 1976, discloses a controlled fluid supply system for an automobile restraint system, one embodiment of which essentially progressively increases the rate of inflation by using principles of differential pressure. In this particular embodiment, there is an outer housing containing pressurized gas and a concentrically positioned inner housing which is essentially divided into three chambers. The first chamber is positioned on the discharge end of the assembly and communicates with the interior of the outer housing through a series of passageways. A shear disk isolates the first chamber from the inflatable member and when ruptured upon detection of a collision, gas flows from the outer housing, through the passageways into first chamber of the inner housing, and into the air bag. A slidable piston-like structure, seated essentially against a portion of the first chamber by a spring within the second chamber, separates the first and second chambers although a restricted passageway through the piston allows limited fluid communication therebetween. Once inflation has been initiated, gas from the second chamber flows into the first chamber and into the air bag. When the forces exerted on the piston by the pressurized gas within the second chamber and biasing spring are exceeded by the force exerted by the pressurized gas in the first chamber on the piston and that force exerted by the pressurized gas in the outer housing on a limited area of an inclined surface of the piston, the piston moves against the force of the spring into the second chamber to expose additional passageways connecting the outer housing and first chamber to increase the flow rate into the air bag. Gas flowing from the outer housing through these passageways exerts additional forces on the piston. As the pressure differential between the outer housing in this region and the second chamber increases, the piston progressively moves further into the second chamber against the force of the spring until it strikes the percussion pin of the percussion ignitor which is positioned within a barrier which separates the second and third chambers. This impact allegedly ignites the propellant contained within the third compartment and the gases generated thereby flow into the outer housing through ports connecting the third chamber and outer housing to further increase the flow rate from the outer housing, into the first chamber, and into the air bag. Although disclosing a variable rate inflation device which utilizes pressure differentials, the flow rate is essentially progressively increased since the flow rate is contingent upon progressive compression of a spring-biased piston. Moreover, the operation of the inflator is quite complex and it would appear that at some point during inflation, the biasing force exerted on the piston by the spring would overcome the forces exerted by pressurized gas in the first chamber and/or outer housing on the piston to close the additional passageways connecting the outer housing and first chamber to inhibit the increased inflation rate.
Japanese Patent Application No. 51-84232, issued July 15, 1976, discloses another air bag actuator which employs pressure differential principles. An outer housing containing a high pressure gas is connected to an air bag but is temporarily isolated therefrom. Positioned within the outer housing is a second housing which is separated into two compartments by a barrier and a piston, the head of which is positioned in the first chamber and biased by a spring against the barrier so that its stem extends through the barrier and into the second chamber. The gas within the second chamber is apparently able to act on the back side of the piston head. Both compartments are fluidly connected with the interior of the outer housing although the passageway for the first chamber is larger than that of the second chamber. As gas flows from the outer housing into the air bag once the isolation is removed, the pressure within the first compartment decreases faster than the pressure within the second chamber due to the difference in cross-sectional areas of the connecting passageways with the outer housing. When a certain pressure differential develops, the piston begins to move against the force of the spring further into the first compartment. After the piston has apparently moved a certain distance, electrodes ignite some type of gas propellant to presumably increase the flow rate into the air bag. Although disclosing a variable rate inflation rate which uses a pressure differential, the gas propellant is ignited by an electrical signal.
Development of air bag inflators of course has not been limited to regulating the flow rate into the inflatable member. For instance, U.S. Pat. No. 4,380,346 to Davis et al., issued Apr. 19, 1983, discloses an inflating apparatus which incorporates certain features to speed up the response of the inflator at low temperatures. The apparatus generally includes an outer housing connected to an air bag and a casing within the outer housing which stores a gas generant composition. A plurality of ports in the inner casing allow for gases generated by burning of the gas generant to flow from the inner casing, into the outer housing, and into the air bag. Initially, some of these ports are covered by single layer of rupturable material while the remaining ports are covered by two layers of the rupturable material to provide the desired temperature compensating feature. When a collision is detected and the gas generant is ignited, the pressure within the inner casing will increase to a level where those ports covered by the single layer will be opened to allow gases to begin f-owing into the air bag. Since only some of the ports are initially opened, the pressure buildup within the inner casing is increased over that which would develop if all ports were initially opened, resulting in faster burning of the gas generant. After a second pressure level is reached, the remaining ports are opened to allow more gases to flow into the air bag. Since the gas generant burns slower at lower ambient temperatures, the built-in pressure buildup feature of the inflator increases the burn rate at these lower temperatures so that the inflator allegedly performs more uniformly and at a maximum pressure over a broader temperature range.
U.S. Pat. No. 4,049,935 to Gruber, issued Sept. 20, 1977, discloses a pressure switch which utilizes a diaphragm to act as an indicator of the operability of the air bag system. This particular apparatus does not direct-y relate to the ignition of a propellant charge or other equivalent which will result in initiation of flow into an air bag. The apparatus is merely directed towards a pressure sensing device wherein by use of a diaphragm, a means is provided to generate a warning signal that the air bag safety device is inoperable in its present condition. In particular, there is a diaphragm which has a constant pressure on one side thereof produced by a volume of gas contained in an isolated reference chamber. The opposite side of the diaphragm is subjected to the pressure of the gas in the cylinder which ultimately flows into the air bag. When the inflating apparatus is operable, the pressure in the cylinder is greater than the pressure in the reference chamber. In such a case, the diaphragm is deflected in a position wherein the apparatus is electrically connected so that if a collision occurs, the inflator will operate to inflate or deploy the air bag by operation of a non-disclosed inflating means. However, if the pressure in the cylinder is reduced below a certain level, the diaphragm will deflect as a result of the pressure in the reference chamber exceeding the pressure in the cylinder by a certain amount. This will result in a separate electrical connection which will generate a warning signal indicating that the inflaring apparatus is inoperable in its present condition.
Although the above-discussed references have each contributed to the useful deployment of air bags, a number of deficiencies still exist, which, if corrected, would provide an improved air bag inflator. An object of the present invention is therefore to provide a plurality of features which are directed toward overcoming these deficiencies, particularly by providing a single, compact apparatus which utilizes a single electrical signal to initiate deployment of an air bag, while still utilizing delayed augmentation of the initial flow rate to fully inflate the air bag. A further object of the present invention is to provide a propellant-augmented inflator which is more simple in construction, has fewer or less expensive component parts, and has all active inflator components on one end of the inflator. Another object of the present invention is to provide an inflator which is more adaptable to programming the gas delivery rate to certain desired criteria and which is temperature compensated to minimize variation in the performance of the inflator due to changes in ambient temperature.